The disclosed embodiments relate to an approach for controlling the stripping of a print media sheet in a fusing system (including a fuser roll and a back-up roll), and, more particularly, to an approach for controlling the dynamic positioning of one or more stripper members relative to a print media sheet exiting the fuser or back-up roll.
The xerographic imaging process is initiated by charging a photoconductive member to a uniform potential. An electrostatic latent image, corresponding with a print job, is then selectively discharged on the surface of the photoconductive member. A developer material is then brought into contact with the surface of the photoconductor to transform the latent image into a visible reproduction. The developer material includes toner particles with an electrical polarity opposite that of the photoconductive member, causing them to be naturally drawn to it. A blank media sheet is brought into contact with the photoreceptor and the toner particles are transferred to the sheet by the electrostatic charge of the media sheet. The toned or developed image is permanently affixed to the media sheet by subsequent application of heat to the sheet. The photoconductive member is then cleaned to remove any charge and/or residual developing material from its surface to prepare the photoconductive member for subsequent imaging cycles.
One preferred fusing method is to provide a heated fuser roll in pressure contact with a back-up roll or biased web member to form a nip. A print media sheet is passed through the nip to fix or fuse the toner powder image on the sheet. In one common example, the heated roll is heated by applying power to a heating element located internally within the fuser roll that extends the width of the fuser roll. The heat from the lamp is transferred to the fuser roll surface along the fusing area. Quartz lamps have been preferred for the heating element.
U.S. Pat. No. 5,822,668 to Fromm et al., the pertinent portions of which are incorporated herein by reference, discloses a fusing subsystem for an electrophotographic printing system in which stripper fingers are shown as being positioned on the “downstream” side of a nip equivalent to the above-mentioned nip. In one known example, the stripper fingers gently strip a fused media sheet from the surface of the heated fuser roll. As taught by the '668 patent, several stripper fingers may be provided adjacent the fuser roll along its longitudinal axis, and each finger may be about 3 mm wide along the length of the fuser roll.
Generally, wax in the toner may be used to facilitate stripping of media for the fuser. This same wax may be used to provide lubrication between one or more stripper fingers and the fuser roll. This sort of lubrication can reduce wear imparted by the stripper fingers on the fuser roll. Avoiding this type of wear is highly desirable since such wear can result in observable print defects (gloss differential and/or poor fusing) and necessitate a replacement of the fuser roll (typically an expensive part). However, there is no guarantee that the toned areas of a media sheet passing through the fuser roll will line up with the stripper fingers in such a way that they are sufficiently lubricated. It would be desirable to provide an approach for ensuring appropriate alignment of stripper fingers and each toned media sheet passing through the fuser roll so that the stripper fingers are sufficiently lubricated and wear of the fuser roll is thereby substantially reduced.